Apparatus for the magnetic levitation and heating of conductive materials



Dec.'29, 1953 P. H. BRACE 2,664,496

APPARATUS FOR THE: MAGNETIC LEVITATION AND HEATING OF CONDUCTIVE MATER:[LS

2 Sheets-Sheet 2 Filed Nov. 25, 1952 ATTORNEY Patented Dec. 29, 1953 APPARATUS FOR y'rims MAGNETIC LEVITA- TION AND HEATING OF CONDUCTIVE MA- T-E-RIALS Porter H. Brace.

Pittsburgh, Pa., assignor `to Westinghouse YElectric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 25, 1952, Serial No. :322,519

(Cl. 219-47l 11 Claims. i

This invention relates to heating and/or melting of electrically conductive materials in any .form and shape while levitated, by a properly distributed alternating magnetic eld or lields in air, vacuum or inert gas, without a confining container or Crucible, as an improvement over that described vand claimed in the Wroughton et al. application, Serial No. 206,344, led January 17, 1951.

Theprincipal object .of my invention, generally considered, is to provide apparatus for heating conductive materials, comprising at least one .but preferably two Velectrical circuits or coi-ls, .means for supplying alternati-ng current to said coil or coils 'to `develop magnetic Aile'lds, whereby a conductive object interposed above the coil, or lower one of the coils and on the common axis thereof, may be levitated and heated by the alternating elds out of contact with a potentially contaminating Crucible or other container.

Another object oi" vmy invention is to improve on the form of the coil or coils employed, by gradually increasing the pitch of the turns outwardly from regions near the axis to those near the periphery or peripheries, thereby lessening 1 the radial field gradient at such places, whereby the melt can more freely increase in girth so that much larger additions can be made thereto before instability occurs.

A further object of my invention is to modify the construction of the coils used for the above stated purpose, by gradually decreasing the pitch .of the coils in the peripheral portionsJ with vthe last few outer turns of the lower or funnelshaped coil on a steepened, or even cylindrical, contour whose maximum diameter is somewhat greater than the outside diameter of a flat or pancake-shaped coil thereabove.

A still vfurther object of my invention is to provide a maximum held gradient and intensity at the neck or lower aperture of the funnelshaped coil, by lplacing thereat a fluid-cooled magnetizable core with a convex top.

An additional object of my invention is to provide additional supporting means for material being heated or melted under the influence of the magnetic fields, above referred to, by providing a jet of material such as helium, argon, hydrogen, mercury vapor, mercury, or other iiuid so that the axial surface of the lower tip of the material melted is supported by such a iet, or cooled so that it remains solid, or both.

Another object of my invention is to form the magnetizable core, above mentioned, from cobaltiron alloy, containing between about 30% and l410% of cobalt and in the form of suitable laminations of, preferably, insulated particles compacted Ato provide Ea coherent mass having va high space factor with minimum eddy-current losses, this preference being based lon the fact 'that the B-H relationship is more nearly linear with such than with `the usual lamina-ted core and, therefore, the phase of the induction through the core will more nearly correspond with that through air.

A further object of my invention is Vto utilize liquid mercury in contact with the .lower tip of the melted material to provide complete throttling action by virtue of its cooling eifect and the hydrostatic support afforded thereby.

A still further object of my invention is to provide apparatus for magnetic levitation and heating of :conductive materials involving Vmeans utilizing the fact that at sufciently high frequencies the now of current induced in a good conductor is a surface phenomenon, to thereby improve the for-m of the magnetic eld generated thereby.

An additional vobject of my invention is to increase the weight of material which can be supported .by lapparatus involving my invention, by

the use of a cage comprising heat-radiating ns surrounding said material during the melting thereof.

Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to the drawing:

Figure 1 is a vertical sectional View of apparatus for producing alternating elds in air, a vacuum, or an .inert gaseous atmosphere, for levitating conductive material to be melted and/or heated, together with means for cooling the coils which develop the fields and the tip of the material `being melted, as well as magnetizable material for plugging the axial apertures in the coils.

Figures 2 and 3 are horizontal sectional views on a larger scale of portions of the apparatus on the correspondingly-numbered lines of Figure 1, in the direction of the arrows.

Figure 4 is a fragmentary vertical sectional view of a por-tion of modified apparatus holding material to be heated.

Figure 5 is a, horizontal sectional view on the line V-V of Figure 4, in the direction of the arrows.

Figure 6 is .a vertical sectional View corresponding with a portion of Figure 1, but showing a modiiication.

Figure 7 ,is a vertical sectional view, corresponding with the portion of Figure 1, but showing another embodiment of my invention.

Figure 8 is a fragmentary vertical sectional view, corresponding With Figure 7, but showing a modification in which the bodies of the intermediate inductors are formed as hollow shells of sheet metal, rather than solid.

The invention here disclosed comprises an inpresent drawings, however, do not show such flattening because of drafting difculties. The two elements I I and I2 are connected in series, as indicated by the tube I3, so that if the direction of current flow in the conical or funnelshaped coil Il may be considered as clockwise, then that in the pancake coil I2 is counterclockwise, assuming both to be viewed from one direction, that is, either from above or below.

The trend of the magnetic fields in the space between the coils will be understood and is indicated in Figure 5 of the application referred to. The suspended melt is indicated at I4, and be considered as metal or other conductive material. It will be noted that the melt is iniprisoned in the weak field region and in space between the coils because of the fact that an isolated conductive mass free to move in a non uniform alternating magnetic field will, in general, migrate in the direction of decreasing field intensity. Now, if, for example, you have a melt Ill, of approximately the indicated shape and additional material is added, the melt will increase in both axial length and girth. This will bring the lower end further down into the neri". portion I5 of the funnel-shaped coil II, although the axial component of the eld is tending toward a maximum, nevertheless the axial field gradient is becoming less. With continuing additions to the melt, a situation will eventually be reached where the electromagnetic forces tending to support the melt will be overcome by the increasing hydrostatic pressure at its lower extremity. Instability then ensues and the melt simply runs downward along the axis of the spout of the furnace I6.

It will be understood that, as in the rst embodiment of the Wroughton et al. application referred to, the furnace I6 may comprise a bell jar I1, formed large enough to enclose the coils II and I2 which are used for levitating conductive material or metal to be melted or heated. This jar, desirably formed of heat-resisting transparent material, such as quartz, or a 96% silica glass manufactured by the Corning Glass Works under the name Vycor, rests on a preferably metal base I8, and may be sealed gas or vacuum tight thereto by suitable means such as a gasket or wax indicated at I9.

The alternating current is supplied to the coils IIand I2 by means of coaxial lines or cables 2l and 22, respectively extending to one end of each coil, the other coil ends being supportingly connected to and through a support member 23. upstanding from the base, and through which water or other cooling medium may be supplied. to the interior of the coils to prevent overheating! The enclosure provided by the bell jar I1 may Liu be evacuated through pipe 24 and, if desired, thereafter supplied with inert gas thereby. In order to place the mass of metal or other conductive material, from which the melt Ill is formed, into the influence of the supporting and heating coils I I and I2, the same may be lifted into place by the cooling device 25, to be subsequently described in detail, or placed on the insulating shield 26 which is disposed above the coil Il, prior to closing the apparatus. A similar insulating shield 21 is desirably provided below, and supported from, the upper coil I2.

The inner portion of the coil II terminates in the neck portion I5, which is generally cylindrical and the turns thereof are helical, as distinguished from spiral-helical for the turns outwardly therev of, that is, toward the periphery. It is my proposal that the pitch of these turns be gradually increased outwardly between the cylindrical generally-axial portion I 5 and the peripheral portion 28, as illustrated most clearly in Figure 1. A similar construction is proposed for the coil l2, that is, between the cylindrical portion 29, in which the turns are helical, and the peripheral portion 3|, the turns are more widely spaced as there illustrated. By such a construction, the radial field gradient will be lessened and the melt I4 can more freely increase in girth so that much larger additions of metal, or other material being treated, can be made before the hydrostatic pressures at the lower tip 32 pass the points of instability.

However, because of the decreased radial eld gradient and the increasing diameter of the melt,

' there arises the danger of radial instability.

This I propose to avoid by a gradual decrease in the pitch of the turns in the peripheral regions 28 and 3l, as illustrated, and by arranging the last few outer turns of the funnel coil II on a steepened or even cylindrical contour, to a maximum diameter somewhat greater than the outside diameter of the pancake coil I2. Thus, the radial field gradient in the circumferential regions of the space between the coils is increased, and also given an axial component that eifectively prevents radial instability at the periphery of the melt.

At the lower tip 32 of the melt I5, there is always some small radius within Which the electrodynamic forces are insumcient to restrain downward axial flow even with very small hydrostatic pressure from the superincumbent molten metal. This is assuming absence of surface ten-v sion, and/or the development of oxide or other films, which tend to avoid breakdown at this point. The steeper the field gradient at the neck of the funnel and the more intense the neld, the smaller will be the radius of what may be considered as an electromagnetic throttle at the neck of the funnel.

I propose to increase both gradient and intensity of the field in that region, by placing within the spout or neck I5 of the funnel coil a fluidcooled magnetizable core 33 of suitably laminated iron, or compacted iron alloy powder, or of compacted ferromagnetic oxide or the like, the upper end of the core being given a convex shape, ellipsoidal or conical, for example, to provide the maximum field strength in the space just above the tip of the core 33.

Although this expedient makes the diameter of the electrodynamic throttle very small, it does not close it entirely and I, therefore, propose -to give positive support by aerodynamic means. For this purpose, I drill the core 33 axially with a relatively small hole 40 through which I may force a cooling'medium such as helium, argon, hydrogen, mercury vapor, mercury or other duid, s0 that the axial .surface of the lower tip of the melt is supported dynamically by the jet of coolant, or cooled so that it remains in the solid state, or both.

If the tip of the melt iskept in solid state, there becomes available for support of the melt at thc axis, the upward component of the electromagnetic forces over the whole area of said tip, in

addition to any jet forces that may be brought to bear, and these forces provide temporary closure of the electromagnetic throttle, even after the jet has been discontinued. short interval during which the core 33 can be removed before the melt I4 hows downward into a mold 34, forexample, here shown supported on a base 35 having legs 36 which rest on the metal base i8.

The core 33, as a specific desirable embodiment, may be prepared from cobalt-iron alloy containing between 30% and 40% cobalt and in the form of suitable laminations or, preferably insulated particles compacted to provide a coherent mass having a high space factor and subject to only small eddy-current losses. The latter factor is important, because the core will usually be called upon to operate at the maximum practicable saturation and at relatively-high frequencies. My preference for thek particular core is based on the fact that the B-H relationship is then more nearly linear than with the usual laminated core and, therefore, the field induced in the core will bemore nearly like that of a field through an air core. Of course, what is really desired is hig permeability air with unlimited saturation.

In order to allow for maneuvering the core 33 and the jet formed therethrough, I mount the coreat the upper end of a hollow shaft 3l carrying a collar 33 adjustably held thereon, as by set screw 39, to prevent an outward movement of said shaft below the bottom of the moldr 34, by engagement with the lower base member 4|. Between the base I8 and the lower base member 4I, I provide a chamber 42, with which the pipe 24 connects for the purpose of evacuating the space in the bell jar Il, through the upper open end of the chamber 42 between the supporting legs 36.

In order to prevent leakage through the lower base member 4l, which seals the lower end of the chamber 42, the upper end of which is sealed to the base it, I provide a gland 43 through which the shaft 3l' reciproca-tes. Undesired upward movement of the shaft 3iA is prevented by a collar 44 held thereon, as by means oi a set screw 45, and engaging the .gland when in the extreme uppermost position, illustrated in Figure 1.

.The coolant is introduced into the hollow shaft 31, as by means of a reciprocable pipe 46 enclosed therein, and connected to a coolant source as by means of a flexible tube 4l. The lower end of the pipe 46 is supported from a bracket 48, secured to the lower side or" the lower base member 4I, as by means of bolts 49. A set screw 5l, or the like, serves to hold the pipe 4t in adjusted position in respect to the bracket 48. A handle 52, secured to the shaft 3l as by means oi a set screw 53, serves for the manipulation of said shaft, allowing it to be raised to the position illustrated in Figure l, or withdrawn so that the core 33 closes the mold 3e, the `coolant passage 43 through said core being, at the same time, closed by plug 49' secured to the upper end of the pipe 46. Passage of coolant around the plug 49', when This allows a inthe position illustrated in Figure 1, is permitted by a transverse passage or port 54 in the pipe 46, allowing the same to pass from the pipe 46 along grooves 55 in the shaft 31, to thereby by-pass the'plug 49.

If desired, the upper or pancake coil I2 may be provided with an otherwise similar but unapertured core 55, which in this case is suspended from the top of the bell jar l1, as from a base 5l secured to said top in a suitable manner indicated at 58.

En an alternative to introducing the material for the melt i4 either by means of the shaft 31 or by having it rest on the insulator 2B, I may initially have such material confined in a cage formed of heat-radiating fins 5|. rihe fins are desirably generally i.sliaped in outline and at the outset their inner edges are preferably fitted into shallow axial slots in the peripheral surface of the main mass oI" metal 14a.

This bird-cage assembly may be supported by an insulating ring 83, by wires 8| from insulated overhead supporting points (not shown), or by other convenient means. The purpose of the cage formed by the ns 6l is to allow melting of the interior portion of the mass I4, while still maintaining control of the molten metal by virtue of the electromagnetic forces acting on it; the surface tension of the exposed liquid metal between the iins; the cooling enect of the iins themselves (due to the fact that they radiate to the water-cooled inductor coils Il and l2, Fig. 1, heat transferred to them by the molten metal), and the action of the adjustable cooling device 225e. 8|a denotes a top skin of solidified material.

The latter is mounted like the device 25 of the rst embodiment, for reciprocation within the furnace and thus may be positioned relative to the bird-cage assembly so as to maintain a skin Bib of solid metal at the lower end of the assembly until such time as 25a is withdrawn downwardly and the skin allowed to melt and so permit the metal to discharge into a mold as, in the first embodiment. By these means there may be exerted a greater control over the mass being melted and provision made for melting a larger amount of material than in the rst embodiment.

The fins may be formed of a suitable refractory material such as molybdenum, tungsten or zirconium, and in one embodiment may be about .05" thick and wide. In many cases the tins may be of the same material as the main body of metal. The fins are spaced close enough together, the distance between adjacent nhs being determined by the surface tension ofthe contained metal when molten, so that the material, even when melted, will not flow out from between them. Except as specifically described, the present embodiment may correspond with the rst embodiment.

In the embodiment of Figure 6, a cooling device, alternative to that of Figure l, is illustrated. Here the magnetizable core 331J is shown provided, not only with an axial aperture 4!)b to allow for the introduction of a cooling arrangement, but the lower portion of said aperture is enlarged, as indicated at 63, to receive the il1us-v trated pipes. The cooling arrangement here consists of a mercury well 64, holding mercury 35, which is cooled by circulation of water through an exterior cooling chamber ES, the water being introduced by the pipe 51 and withdrawn by the pipe S8.

Mercury is introduced to or Withdrawn from well as by means of pipe It will be seen that the top of the mercury 65 contacts the lower tip of the melt Mb freezing it as indicated at 32h, thereby accomplishing the effect contemplated by the aperture ri illustrated in Figure 1. Except as specifically described for the present embodiment, the same may correspond with the first embodiment.

In the induction melting system previously described, the magnetic fields produced are somewhat irregular because the current flows in definitely separated channels instead of as smooth sheets. I propose, in the embodiment of my invention of Fig. 7, to improve on this situation by making use of the fact that, at sufficiently-high frequencies, the ow of current induced in a good conductor, such as copper or silver, is a surface phenomenon.

If I take a primary inductor coil and place Within it as an intermediate inductor a copper or other highly-conductive block, having a corresponding outer surface adapted to t within the coil, and an interior heating chamber, whose contour is adapted to effect suspension melting, like the arrangement of Fig. l, and a thin radial slot that compels the induced current to flow inwardly and around the walls of the chamber, I obtain a smooth current sheet and automatically a desirable distribution of current. This is because the distribution of said current on the walls of the cavity will be -most dense in the regions of minimum diameter, just where it is needed to force the flux through the restricted area, because the inductance per unit of axial length is less and the current adjustsl itself so that the reactive electromotive force is the same at all levels.

Instead of a single slot, designated 12, in the copper or silver intermediate inductor 7l, there may be two or more of such slots, the individual inductor blocks provided with passages (not shown) for the flow of coolant, and the whole assembly mechanically bound together by the primary inductor coil 13, but separated therefrom by insulation, such as mica or the like. An

additional primary inductor coil 14, above the coil 13, is desirably provided for a more complete enclosure of the furnace or melting chamber 15, in which is shown a melt Ill.

Thus, in Figure 7 I'show a pair of inductive field-producing coils 'i3 and l corresponding generally with those designated with l! and l2 in Figure l. Within these coils are sheets of insulation 'i6 and 11, respectively separating them from their cooper intermediate inductor cores 1I and 18. The assembly, as illustrated, is supported from a, base (not shown) as by means of standards 19. A suitable cooling and/or lifting device c is provided, as in the other embodiments. Except as is specifically described for the present embodiment, the same may correspond with the rst embodiment.

'Although Fig. 7 shows solid copper or silver blocks I have already noted that these blocks which may be termed secondary inductor may.

be provided with passages for water or other coolant. Alternatively, instead of shaping the intermediate inductors from solid metal, they may be made in the form of shells, as indicated in Fig. 8, in which parts corresponding with those of Fig. '7 are indicated by similar `reference characters with the sufx d, whosesupercial contours are substantially the same as those of corresponding solid inductor blocks, whose minimum wall thickness is preferably at least equal to the depth of penetration D of the induced currents, and whose maximum thickness need be no more than 4 or 5 times the minimum, insofar as electrical requirements are concerned. The depth of penetration D is the radial distance between the surface of, say, a cylinder surrounded by a coaxial solenoid and thereby subjected to an axially-directed alternating magnetic field, and that imaginary internal cylindrical surface, concentric with the outer one, Where the current density is equal to the surface density divided by e, where e is the base of the Naperian system of logarithms. The numerical value of e is 2.718.

The numerical value of the depth of penetration, D, is dependent on the frequency of the alternating magnetic field as well as the electrical conductivity and magnetic permeability of the material in question and may be calculated with sufficient accuracy for engineering purposes from the formula f l 2m/fpm 1o-9 where D=depth of penetration in centimeters.

f=frequency of the applied (sinusoidal) magnetic eld, in cycles per second n=magnetic permeability of the material=1 for copper, silver and other non-magnetic materials, and

a=electrical conductivity in reciprocal ohm centimeters For copper at room temperature and a frequency of 9600 cycles/second (a frequency widely used for inductive heating work) D=.067 cm.

As actually, current does ow at depths greater than D, some advantage may be gained by making the wall thickness greater than D. However thicknesses greater than 4D show little advantage from the electrical standpoint, although they may be desirable for mechanical reasons.

I may fabricate shell-type intermediate inductors 1 ld, as illustrated in Fig. 8, from suitable sheet metal by conventional means e. g., welding, brazing or casting around suitable cores or by electrodeposition of copper or silver, for example, on suitable forms made of wax or a low-melting metal that can be melted and drained away, leaving the electrodeposited metal in the form of a hollow shell. I may remove unwanted heat from such shell-type intermediate inductors by injecting a fluid coolant, e. g. Water or air, or such other liquid or gas as circumstances may dictate into the space within the shell, as by means of pipes connected thereto, one of which is shown at 82 and the other of which desirably extends from a remote portion of the shell 14d. The other shell, not shown, but corresponding with the intermediate inductor 18, may be cooled in a similar manner.

From the foregoing, it will be seen that I have provided an improved apparatus, for the magnetic levitation and heating of conductive materials, in the form of an induction furnace, several embodiments being disclosed. It will be understood that the system is generally like that disclosed in the Wroughton et al. application,previouslyidentied, except that improvements have been devised involving the non-uniform spacing of jthe turns of the induction coils, the employment of one or more magnetizable plugs or blocks, the provision of novel levitating and/or cooling means which pass through a Crucible or mold for catching the rent because oi high frequency being in the skinof the intermediate inductor at the desired position with respect to the melt, or material being levitated and heated. l

Although preferred embodiments or my invention have been disclosed, it will Le understood that modifications may be made within thespiiit and'sc'ope of the invention.

I claim: v y

1. Apparatus forlevitating, heating and melting electrically conductive materials, comprising aV conductive tube helically bent into a coil of upwardly expanding generally frusto-conical form, means for supplying alternating current to said tube to generate' a levitating magnetic lield -r thereabove, means for internally cooling said' tube, and means for moving a conductive object into the influence of said field whereby it may be levitated while heated to the desired extent, the

pitch of the turns of said coil being greater in regions intermediateV the periphery and axis, than the pitch of the peripheralV and axial turns, in order to lessen the eld gradients at such regions, so that a conductive object in the influence of said eld can upon melting more freely increase in girth, so that much larger additionsv of conductive material can be made to the melted material before instability occurs.

2. Apparatus for levitating, heating and melting electrically conductive materials, comprising a conductive tube helically bent into a coil of upwardly expanding generally frusto-conical form, means for supplying alternating current to said tube to generate a levitating magnetic field thereabove, means for internally cooling said tube, and means for moving a conductive object into the inuence oi said iield whereby it may be levitated while heated to the desired extent, the pitch o1" the turns of said coil being greater in regions intermediate the periphery and axis, than the pitch of the peripheral and axial turns, in order to lessen the iield gradients at such regions, so that a conductive object in the iniiuence of said field can upon melting more freely increase in girth, so that much larger additions of conductive material can be made to the melted material before instability occurs, the pitch of the turns of said coil being gradually decreased in said peripheral turn with the last few outer turns on a steepened contour to increase the radial iield gradient and eiectually prevent peripheral instability of the melt.

3. Apparatus for levitating, heating and melting electrically conductive materials, comprising a conductive tube bent into a spiral coil with turns thereof lying in a generally horizontal plane, another similar tube helically bent into a coil of upwardly expanding generally frustoconical form coaxial therewith, having an outside diameter larger than that of the said rst mentioned coil, and lying therebeneath, means for supplying alternating current to said coils in series to generate opposed levitating alternating magnetic elds, the pitch of the turns of said coils being greater in regions intermediate the peripheries and axis than the pitch of the peripheral and axial turns in order to lessen the rleld gradients at such regions, so that a conductive objectv in the influence of said eld can upon melting nioreireely increase in girth, so that much larger additions of conductive material can be made to the melted material before instabilityr occurs. Y

4. Apparatus for levitating, heating end melting electrically conductive materials, comprising a conductive tube bent into a spiral coil andY with turns thereof lying in a generally horizontal plane, another similar tube helically bent into a coil of upwardly expanding generally frustoconical form coaxial therewith, having an outside diameter larger than that of the said first mentioned coil, and lying therebeneath, means for supplying alternating current to said coils in series to generate opposed levitating alternating magnetic elds, the' pitch of the turns of said coils being greater in regions intermediate the peripheries and axis than the pitch of the peripheral and axial turns in order to lessenr the iield gradients at such regions, so that a conductive object in the iniluence of said field can upon melting more freely increase in girth, so that much larger additions of conductive material can be made to the melted material before instability occurs, the pitch of the turns of said coil being gradually decreased in said peripheral turns with the last few outer lower coil turns on a steepened contour to increase the radial eld gradient and effectually prevent peripheral instability of the melt;

5. Apparatus for levitating, heating, and melting electrically-conductive materials, comprising a conductive tube helically coiled from a lower opening to upwardly-expanding frusto-conical form, a similar tube spirally coiled with its turns lying in a plane over the turns of said rst tube and coaxial therewith, and a magnetizable core, the upper surface of which is convex, disposed on the axis of said helically coiled tube and closing the lower opening therein, to provide maximum held strength in the space above said lower openmg.

6. Apparatus for levitating, heating and melting electrically conductive materials, comprising a conductive tube helically coiled from a lower opening to upwardly expanding frusto-conical form, a similar tube spirally coiled with its turns herewith, and a magnetizable core formed of between 30% and 40% cobalt and the rest iron as isolated particles compacted into a coherent mass having a high space factor and subject to only small eddy current losses, the upper surface of which core is convex, said core being disposed on the axis of said helically coiled tube and closing the lower opening therein.

7. Apparatus for levitating, heating and melting electrically conductive materials, comprising 8. Apparatus for levitating, heating and melting electrically conductive materials, comprising shaped in outline and provided with lower angular extensions, a cooling device mounted for Vertical reciprocation, the inner ends of said extensions being adjacent the top of said cooling device, the spacing of said fins being such that material held within the cage formed thereby will be retained because of its surface tension even when molten.

` 9. Apparatus for levitating, heating and melting electrically conductive materials, comprising a conductive tube helically coiled to upwardly expanding frusto-conical form, means for supplying alternating current to said tube to generate a levitating magnetic eld thereabove, and means disposed axially below said helically coiled tube for engaging the lower tip of material melted and supported above said coil, said means comprising a magnetizable core tting within the interior turns of said tube, said core being provided with an aperture, a cooling arrangement received in said aperture and consisting of a mercury well, mercury in said well, a chamber external to said well, and means for circulating a cooling medium in said chamber for keeping said mercury cool to avoid substantial loss thereof when engaging the lower tip of material supported in the field above said coil and melted thereby.

10. Apparatus for levitating, heating and melting electrically conductive materials comprising a conductive tube helically coiled to upwardly expanding frusto-conical form, a highly-conductive intermediate inductor block having a corresponding outer surface, fitting within said coil and spaced therefrom by insulating means, said intermediate inductor block being so shaped as to dene an interior heating chamber whose contour is adapted to effect suspension melting, and a thin radial slot which compels high-frequency current when induced in said block to flow inwardly and around the walls of the chamber to obtain a smooth current sheet on the interior surface of said chamber, in order to effect desired inductive action on conductive material disposed in said chamber, when the coil is energized by high-frequency current passing therethrough.

11. Apparatus for levitating, heatingand melting electrically conductive materials comprising a conductive tube helically coiled to upwardly expanding frusto-conical form, a similar tube helically coiled to downwardly expanding form, with its turns lying over said first tube and coaxial therewith, a highly-conductive intermediate inductor shell having a corresponding outer surface, fitting within said lower coil and spaced therefrom by insulating means, a highly conductive intermediate inductor block having a corresponding outer surface, tting within the upper coil and spaced therefrom by insulating means, said intermediate inductor shell being so shaped as to denne an interior heating chamber whose contour is adapted to effect suspension melting, and a thin radial slot which compels high-frequency current when induced in said intermediate nductor shells to flow inwardly and around the walls of the chamber to obtain a smooth current sheet on the interior surface of said chamber, in order to effect desired inductive actionv on conductive material disposed in said chamber, when the coils are energized by high-frequency current passing therethrough, and pipes connected to said shells for circulating cooling fluid through the interiors thereof.

PORTER H. BRACE.'

No references cited. 

